Lets Do Wine Posting Page
Monday, November 19, 2007
I've noticed in some of the bottom of my bottles of wine there seems to be almost like a granual of sugar. They look like diamonds. What would cause this and is the wine safe to drink?

Grapes naturally contain several organic acids including tartaric acid . They also contain potassium and calcium ions which form salts with the organic acids. As you may already be aware, these salts can precipitate out of the wine to form a material called potassium (calcium) bitartrate. This is a clear (sometimes red or brown), crystalline material. They are also referred to as wine crystals or diamonds, but vintners also call them 'tartrates'. These bitartrate salts have several interesting physical properties. In the unfermented grape juice only little can be dissolved
(1). Even less is soluble in the juice (wine then) after fermentation, since alcohol can dissolve less of it
(2). The quantity of potassium bitartrate dissolved in wine is also strongly temperature dependent
(3). Cold wine cannot hold as much bitartrate as warm wine hence even more tartrates will drop out. Having said that you can get `dropout` at higher temperature, albeit at a slower pace.

In combination, these three properties produce an interesting winemaking problem. Generally, grape juice contains all the bitartrate it can hold when the grapes are picked. Alcohol begins to accumulate when the grapes are fermented. As the alcohol concentration increases, the new wine becomes saturated, and tartrate precipitates out of the wine. As fermentation continues, more alcohol is produced, and more tartrate is forced to precipitate out of wine. By the end of fermentation, the new wine is over-saturated with tartrates. The tartrate continues to drop out of the solution, but at normal cellar temperatures, tartrate precipitation is very slow. Often the tartrate crystals continue to precipitate for a year or more. As tartrate drops out of solution, suspicious looking crystals are formed in the bottle, or dense sediments form. Tartrate sediments are unsightly, and are sometimes mistaken for glass particles. However, they are in no way harmful nor do they spoil the wine. When a wine kit contains more juice, chances of acid instability is higher. So we regard a tartrate dropout more of a sign of quality than a problem or an issue. Commercial wineries cold stabilize their wines to avoid tartrate dropouts. But since the more stable Calcium bitartrate is less effected by temperature it can occur even in the best cold stabilized wines.

by: Lets Do Wine